[Elecraft] [KX3] Noise blanker comments

[David Anderson]

I promised to record an example of rain static on 144 MHz that defeats the noise blanker on the KX3, but which a wideband SDR receiver can almost entirely eliminate. As Wayne explained this is to be expected, but he was interested in seeing if things could be improved.

So I have two short but large I/Q recordings made with HDSDR (note not ordinary audio files) centred on 144.500MHz and in there we have a weak beacon on 144.482 MHz CW which keys and also sends JT65B at times in one of the recordings. There is also a strong radiated birdie which is from the KX3 which was on at the time on 144.400 MHz. The rain static is intermittent so you may hear those weak signals when the static is gone. The HDSDR software can eliminate the static if its RF NB is switched on and the level adjusted.

I suggest that the free software HDSDR be used to replay the files. 

The two files are:

1. JT65B beacon example
https://drive.google.com/open?id=0Bx7H6CQsV80hU2FpeGdxTWlEWXc


2. CW beacon example
https://drive.google.com/open?id=0Bx7H6CQsV80hV2I3dlVBb0ZvM28


I hope the files will be of some value.

Best wishes and a prosperous 2016 to all at Elecraft.

David GM4JJJ


> On 11 Dec 2015, at 18:55, David Anderson <gm4jjj at yahoo.co.uk> wrote:
> 
> Wayne,
> 
> Many thanks for the comprehensive reply.
> 
> Next time I encounter the static rain/snow that completely overwhelmed the KX3 noise blanker, I will make a short wide band RF recording from the SDR and can send you a link to the file which may help with developing other DSP noise blanking algorithms.
> 
> I do agree the existing KX3 noise blanker does a great job on other types of pulse noises, and doesn't suffer much when used in the presence of other strong signals on the band. Much much better in that respect than my previous transceivers.
> 
> For now I am happy to use the KX3 in tandem with the wide band SDR when I need to blank out the rain static on 144 MHz which happens from time to time.
> 
> 73 from David GM4JJJ
> 
>> On 11 Dec 2015, at 15:48, Wayne Burdick <n6kr at elecraft.com> wrote:
>> 
>> David,
>> 
>> The KX3's noise blanker is implemented entirely within its DSP. Ahead of the DSP are the mixer and its duplexer, which have a finite bandwidth, and possibly the roofing filters, which have much narrower bandwidths. Because of this, there's no way for the DSP to gain access to wideband data for blanking purposes. 
>> 
>> While this does reduced effectiveness on some types of noise, the blanker still works well on most. I use it every day at my QTH on noise ranging from telephone-pole ESD to appliances and computer peripherals. And because the blanker is strictly operating within a narrow bandwidth, it cannot easily be "pumped" by signals well outside the IF passband.
>> 
>> The KX3's narrowband filtering also gives it a big advantage in blocking dynamic range compared to other SDRs that have nearly unlimited input bandwidth. For example, Sherwood measured the KX3's BDR at 138 dB, compared to something in the low to mid 120's for "pure" SDRs. The KX3 is also fifth on Sherwood's list for 2-kHz IMDDR3, again because of the narrow roofing filter.
>> 
>> Since the DSP controls blanking, it may be possible to implement additional noise blanking algorithms in the future. That is definitely on our list. If you send us a detailed description of the types of noise you encounter, we could try to duplicate them in the lab during this effort.
>> 
>> 73,
>> Wayne
>> N6KR
>> 
>> 
>>> On Dec 11, 2015, at 3:59 AM, David Anderson <gm4jjj at yahoo.co.uk> wrote:
>>> 
>>> Still interested in any comments about how the KX3 noise blanker is implemented, and if it could be improved to make it as effective as the wide band RF blanker in HDSDR.
>>> 
>>> I now have the SDRPlay tracking the KX3 VFO so that in the event of static rain QRN I can switch to the SDRPlay for good copy when the KX3 is useless.
>>> 
>>> 73 from David GM4JJJ
>> 
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